For this axis, we had a model in which, when the limb was growing, cells near the tip were in a special region, which we called the Progress Zone and cells were continually leaving the Progress Zone and they measured how much time they spent there. If they spent a very short time there, they would make this structure; if they spent a long time there, they’d be at the tip of the digits. And we did do various experiments that fitted with this quite... quite nicely and...  however, even today, the experiment or the... the model, is really quite controversial. A friend of mine who is a professor of genetics in Harvard — Cliff Tabin — really doesn’t accept the model at all and I don’t accept his objections to the model. And this one model here with a signal from this region here setting up a gradient as Cheryll Tickle has shown, is really much more complicated than... than we originally thought. But nevertheless, it’s... it’s not too bad and we really had a... a very enjoyable time working this out. However, I must say that when we come to positional information in general, we still really are pretty ignorant of the molecular basis and although Francis Crick had put forward the idea that the way cells would know their position, would be with making a molecule here and then diffusing, you know, diffusing along, this would tell the cells where they were... in fact, I’ve just written a paper with my friend Michel Kerszberg, saying that diffusion is just too unreliable a mechanism for giving cells their positional identity and cell... direct cell-to-cell contact in some really quite complex way, would be a much better way of doing it. But it’s an un... it’s a largely unresolved problem.